Krishna P. Woli1, Sudipta Rakshit2, John P. Lundvall3, John E. Sawyer1 and Daniel W. Barker4, (1)Department of Agronomy, Iowa State University, Ames, IA (2)3500 John A. Merritt Blvd, Tennessee State University, Nashville, TN (3)Lundvall Farms, Ames, IA (4)Iowa State University, Iowa State University, Ames, IA
Liquid swine (Sus scrofa domesticus) manure (LSM) is a valuable source of plant nutrients to be utilized for crop production. However, there has been no study investigating the N response of corn (Zea mays L.) to potential residual N effects of LSM applied to a preceding soybean [Glycine max (L.) Merr.] crop. Objectives of this study were to evaluate response of soybean to LSM application, potential for post-harvest soil profile NO3-N accumulation, and residual-year LSM N response in corn. On-farm trials were conducted at eight different sites across Iowa from 2000 to 2003. Three application rates of control, low, and high LSM were applied to soybean. In the following year corn, four fertilizer N (FN) rates were applied within each prior-year LSM rate. The LSM significantly increased soybean grain yield (GY) at 63% of sites, with no GY reduction at any site. Post-soybean harvest soil profile NO3–N increased at four sites with LSM application, with a mean across site 12 and 24 kg NO3–N ha-1 increase for the low and high LSM rates, respectively. Residual-year corn GY was increased at 71% of sites from the prior-year LSM N application. Corn leaf relative chlorophyll meter (RCM) values were also increased with the prior-year LSM N, and end of season lower corn stalk NO3–N (CSNT) increased with the prior-year LSM, but only when FN was also applied. The residual-year N supply to corn was estimated at 11% of the total LSM-N applied to soybean using the GY and RCM responses to FN rate, approximately the mean post-soybean harvest profile NO3–N ha-1 increase with each LSM rate. Liquid swine manure application to soybean can be a viable nutrient management practice; however, total-N application should be at a rate to minimize residual NO3–N buildup and carryover to future crops.